1. Field of the Invention
This invention concerns polymeric perfluoroetheracyl peroxides, and an improved process for making them.
Selected high molecular weight fluorocarbon and perfluoroether peroxides have been known in the art for a number of years. The synthesis of these compounds has generally involved the reaction of aqueous peroxide with an acid halide. Using this method, some of the acid halide is converted to carboxylate salt. As the molecular weight of the carboxylate salt increases, soaps and stiff emulsified gels are formed that interfere with the isolation of the pure compound. Conventional methods of isolating the peroxide have involved treatment of the mixture with sulfuric acid and following up the procedure with centrifugation to separate out the peroxide. See, e.g., U.S. Pat. No. 3,882,193. The present invention improves upon prior art procedures for synthesizing oligomeric peroxides by limiting the presence of water so as to retard emulsion and gel formation and result in the direct formation of a liquid product containing the high molecular weight perfluoroether peroxides. This invention also concerns novel polymeric peroxides produced by the present process, and a novel method of coating substrates with fluoropolymers using the polymeric peroxides.
2. Discussion of the Prior Art
U.S. Pat. Nos. 2,559,630 and 2,792,423 disclose polymeric perfluoroalkylacyl peroxides and a method for making them. The chemistry used in the process to produce the acyl peroxides is the reaction of the corresponding acyl halide (usually fluoride or chloride) with a peroxide under basic conditions. The peroxide can be added as hydrogen peroxide and a base such as sodium hydroxide added, or the base and peroxide can be combined in one compound such as sodium peroxide. The reaction is often done in a heterogeneous system containing water to dissolve the inorganic salts, and an organic solvent to dissolve the perfluoro polymer.
U.S. Pat. Nos. 3,810,875 and 3,882,193 disclose polymeric perfluoroether acyl peroxides wherein both ends of the perfluoroether polymers end in peroxides, and each "block" of perfluoroether polymer is part of a larger polymer molecule joined by peroxide linkages. Thus, such poly(perfluoroether)acyl peroxides are "difunctional", that is reactive on both ends of the perfluoroether blocks. The same basic chemistry described above was used to prepare the peroxides.
Z. Chengxue et al., in Journal of Organic Chemistry, vol. 1982, pages 2009-2013 describe the decomposition of perfluoroacyl peroxides for both perfluorocarbon and perfluoroether compounds, but the molecular weights of the perfluoro segments are very low.